Fusible protective device



Dec 3, 1940. w 2,224,111

FUSIBLE PROTECTIVE DEVICE Filed July 14, 1938 Invenior.

Patented Dec. 3, 1940 UNITED- STATES PATENT OFFICE Chase-Shawmnt Com a corporation of Application July 14,

24 Claims.

This invention relates to thermal cut-outs or fusible protective devices characterized by employing a low melting temperature mass of metal, and means for melting the mass to eifect the release of a movable circuit interrupting member and the consequent interruption of the circuit.

The primary object of the present invention is the provision of a simple reliable device of the type set forth that is capable of being radially and economically manufactured in quantities and under conditions that provide for substantially identical performance of devices intended to have the same ratings.

Fig. 1 is a side elevation of a fusible protective device embodying the present invention.

Fig. 2 is a plan view of Fig. 1 with the end cap .removed.

Fig. 3 is an enlarged section taken along line 3-3 of Fig. 2.

Fig. 4 is a perspective view of the circuit conducting elements of the device of Fig. 3.

Fig. 5 is a sectional view similar to but at right angles to Fig. 3 illustrating a modified form of the current conducting elements.

Fig. 6 is a sectional detail taken along line 66 of Fig. 5.

The fusible protective device embodying the present invention and chosen for purposes of iilustration is of the plug fuse type and includes a 30 cylindrical body I 0 of insulating material, as porcelain, having an internal chamber l2 open at the top and closed by the bottom wall It through which a tubular center contact member it of a more or less common type is extended.

35 The open upper end of the chamber is closed by a transparent closure disc It, usually mica, re-

tained in place by a metal end cap 20 the side wall of which is crimped over the outstanding flange 22 of the plug body. The plug body is provided with external screw threads II on which an internally and externally screw-threaded metal terminal shell 26 is threaded.

The construction of the plug body and the terminals is not herein of particular importance, except as noted in the claims, as the invention resides more specifically in the current conducting elements disposed within the plug body.

The current conducting elements include a supporting rod 28, a movable conductor 30, and a mass 32 of low melting temperature metal. The supporting rod 28 comprises a length of wire or ribbon preferably sufllciently stiff to be selfsupporting and to support the parts attached thereto in the position illustrated. The lower part or shank 29 of the wire or rod is straight and pony, Ncwburyport, Mm,

Massachusetts 1938, Serial No. 219,224

is retained within the inner tubular end of the center contact I by a mass of high melting point solder 34. The upper end of the rod has a horizontally reflexed end portion 36 providing a hook on which the readily fusible metal mass 32 is disposed. The metal mass 32 preferably is cylindrical and has a central bore into which the hook 36 is pressed but is otherwise free, that is to say, it is not retained in any retaining cup or the like supporting means.

The conductor 30 is flexible and preferably is a copper strip forming a heater for the fusible mass and also a fuse link and is provided with a most readily fusible portion by a perforation 38 or the equivalent. The outer end of the fuse link is located in a vertical channel in the side wall of the plug body filled with cement 40 and electrically and mechanically connected to the screw shell 26 by a mass of high melting temperature solder 42. The fuse link extends crosswise' of the plug chamber l2 and downwardly and its inner end 43 is bent substantially vertically downward and is abutted against the end of the fusible mass 32 and is attached to the mass by applying a hot iron to the link thereby melting the metal in the end face of the fusible mass and causing it to be bonded to the link.

The fusible link above the perforation 38 is provided with a transverse channel 44 in its under face in which the horizontal end 46 of a wire spring 48 is located, the other end of the spring being located in a socket 50 formed in the upper end of the plug body. The spring is arranged to exert an upward tension on the link and to move the link in a circuit opening direction into some position as illustrated by the dotted lines Fig. 3 remote from the fusible mass when the bond between the link and the fusible mass is suiiiciently loosened, thereby interrupting the circuit through the device. When the link itself fuses at the perforations 38 by reason of an abnormally high current the spring 48 moves the link into the same position thereby enlarging the circuit interrupting gap.

The fusible metal 32 is sufficiently big in diameter and long to absorb a substantial amount of heat so that the device can be traversed by a moderate overload for a substantial period of time before the heat developed in the link and accumulated in the fusible mass raises the temperature sufliciently high to loosen the bond between the link and the mass and effect the interruption of the circuit. When, however, the device is traversed by a heavy overload on short circuit current the fuse link is adapted to blow and interrupt the circuit before the fusible metal can fuse and effect the opening of the circuit.

The'fusible link 30 constitutes the heater for the fusible mass and the mass ordinarily fuses on the end face thereof at the junction between the mass and the fuse link. The rod 28 constitutes a thermal resistor to prevent undesirable loss of heat from the fusible mass to the center contact as conditions governing the loss of heat from the center contact in different sockets in which the device might be screwed is out of the control of the manufacturer of the interrupting device. The rod 28 can be made of any suitable material that will provide a desirable temperature 15 difference between its ends.

is very satisfactory not only because it has considerable thermal resistance but also because it is stiff. A copper wire also can be used. The length and cross section of the rod will, of course, be adjusted to provide the desired thermal drop for the metal employed. The hook formation of the wire is desirable in that it permits a relatively long length of wire to be used so that the thermal drop between its ends is substantial and small manufacturing variations, such as variations in the height of solder 35 on the rod 28, do not materially influence the calibration of the device. The hook formation together with the inclination of the fuse link keeps the fusible mass on the wire regardless of the position of the device when it is'installed in a socket although the fusible mass becomes soldered to the end of the hook in the act of fusing the mass to the fuse link.

In the modification illustrated in Figs. 5 and 6, the fuse link and the supporting rod instead of being fused to the fusible mass is crimped thereto or is compressed thereon. In this instance the mass 32a has a slot 52 in which the 40 end part 36a of the support and the end part 54 of the fusible link are located after which the fusible mass is pressed into firm mechanical holding pressure with the link and hook. The hook can have a flattened part 56 the more securely 45 to retain the fusible mass thereon. The end of the link can be similarly arranged although this is not essential.

In operation on low overloads the fusible mass fuses at its region of contact with the link so that 50 the spring can pull the link end out of the mass and upwardiy into a circuit interrupted position in the manner heretofore explained.

I claim: 4 1. In a fusible protective device, a conductive 55 element comprising a rigid thermally-resistive conductor anchored at one end, a free readily fusible pre-formed mass on and enclosing and supported directly by the other end of said conductor, a flexible heating conductor attached to 0 said readily-fusible mass and releasable therefrom upon the fusing of said mass, and means responsive to the fusing of said mass to flex said flexible heating conductor away from said mass.

2. In a fusible protective device, a fusible mass, a stationary support constituting a thermal resistor carrying said mass at one end, a massheating conductor bonded to said mass, and means for separating said mass and heating conductor upon release of the bond therebetween.

3. In a fusible circuit interrupter, a rigid supporting hook, a pre-formed fusible mass supported bysaid hook, a conductor releasably attached to said fusible mass, and means responsive to the release of said attachment due to the fusing of 75 said mass to remove said conductor therefrom.

A steel alloy wire 4. In a fusible conductor, a fusible mass, 8. supporting rod having one end embedded in and thereby directly supporting said fusible mass, a heating conductor attached to said fusible mass and releasable therefrom upon the fusing of said mass, and means responsive to the fusing of said mass for separating said conductor and said fusible mass.

5. In a fusible circuit interrupter, a body containing a chamber, a rigid support extended longitudinally of said chamber and having a part extended transversely thereof, a fusible mass on said transverse part and supporteddirectly thereby, a heating conductor adherent to said fusible mass and releasable therefrom upon the fusing of said mass, and means for separating said conductor and mass upon the fusing of said mass.

6. In a fusible circuit interrupter, a body containing a chamber, a rigid support extended longitudinally of said chamber having an end part extended transversely of said chamber, a tubular fusible mass threaded on said transverse part, a.

heating conductor adherent to said tubular fusible mass and releasable therefrom upon the fusing thereof, and means responsive to the fusing of said mass for separating said conductor and fusible mass and interrupting the circuit through the interrupter.

'7. In a fusible circuit interrupter, a body containing a chamber, a support extendedlongitudinally of said chamber having an end part extend ed transversely of said chamber, a tubular fusible mass on said transverse end part and supported directly thereby, a conductor fused to an end face .of said tubular. mass, and means responsive to the porting rod anchored at one end. and having a separating tension-between said conductors and.

fusible mass.

11. In a fusible circuit interrupter, a body containing a chamber, a contact member on the end of said body. a supporting rod having one end part fixed to and supported rigidly by said contact member and extended longitudinally of said chamber and having a, reflexed free end part disposed crosswise of said chamber, a fusible mass supported by said reflexed end part, a conductor attached to said fusible mass and releasable therefrom upon the fusing thereof, and means connected to said body and to said conductor responsive to the fusing of said mass for separating said conductor and mass.

12. In a fusible circuit interrupter, a body con-- taining a chamber, a contact member on the end of said body, a supporting rod having one end part fixed to said contact member and extended longitudinally of said chamber and having a reflexed free end part disposed crosswise of said chamber, a tubular fusible mass on said free end, a conductor fixed to the end face of said fusible mass, and means responsive to the fusing of said mass for separating said mass and conductor.

13. In a fusible circuit interrupter, a supporting rod, a rigid anchorage for one end of said rod, a pre-formed fusible mass on and enclosing and engaging the other end of said rod, a conductor attached to said fusible mass and releasable therefrom upon the fusing thereof, and separate conductor tensioning means.

14. In a fusible circuit interrupter, a chambered enclosing body having center and annular contacts, a supporting rod carried by and extended upwardly in said chamber above said center contact, said rod having a hook at its free end which is disposed crosswise of said chamber, a pre-formed fusible mass on and surrounding said hook, a conductor attached to said fusible mass and releasable therefrom upon the fusing thereof, and means responsive to the fusing of said mass for separating said mass and conductor.

15. In a fusible circuit interrupter, a chambered enclosing body having center and annular contacts, a supporting rod carried by and extended upwardly in said chamber above said center contact, said rod having a hook at its free end which is disposed crosswise of said chamber, a pre-formed fusible mass on and surrounding said hook, a conductor fused to said fusible mass, and conductor-tensioning means responsive to the fusing of saidmass for separating said conductor and mass.

16. In a fusible circuit interrupter, a support, a conductor, a fusible mass carried by said support and crimped about said conductor, and conductor tensioning means independent of the conductor operative to interrupt the circuit through the interrupter in response to the fusing of said mass.

17. In a fusible circuit interrupter, a support, a fusible mass crimped about said support, a fusible conductor attached to said fusible mass and releasable therefrom upon the fusing thereof, and means responsive to the fusing of said mass for separating said conductor and mass.

18. In a fusible circuit interrupter, a support, a conductor, a fusible mass crimped about and onto said support and conductor, and means for separating said conductor and mass in response to the fusing of the latter.

- 19. In a fusible circuit interrupter, a body containing a chamber, a support having a fusible mass located in said chamber and having a face spaced from a side of said chamber, a conductor fused to that face of said fusible mass, and spring means disposed above said mass for moving said conductor away from said fusible mass in the space between said mass and wall of said chamber and crosswise of said chamber in response to the fusing of said mass.

20. In a fusible circuit interrupter, a supporting member having rigid anchoringmeans for one end and free at the other end and composed of a thermal resistance material, a fusible metal mass on and supported by the free end of said supporting member, and a heating conductor attached to said fusible mass and releasable therefrom upon the heating of said conductor and the fusing of said mass, and means for separating said heating conductor and mass upon the fusing of the latter.

21. In a fusible circuit interrupter, a relatively thermally insulated fusible mass, a heating conductor attached to said fusible mass and releasable therefrom upon the fusing of said mass, and means responsive to the fusing of said mass for separating said mass and heating conductor.

22. In a fusible circuit interrupter, a fusible mass, supporting means therefor characterized by opposing conduction of heat therethrough from said mass, a heating conductor attached to said fusible mass and releasable therefrom upon the fusing of the latter, and means responsive to the fusing of said mass for separating said mass and heating conductor.

23. In a fusible protective device, terminals, a fusible mass, a thermally resistive electrically conducting support for said mass and one terminal, a heating conductor connected to said other terminal and attached to said fusible mass and releasable therefrom upon the fusing of said mass, and means for separating said heating conductor and mass upon the fusing of the latter.

24. In a fusible circuit interrupter, a fusible mass, a terminal, a support carrying said mass at one end and connected at its other end to said terminal and composed of thermally resistive material and being relatively long between said mass and terminal to oppose conduction of heat from said mass to said terminal, a second terminal, a heating conductor connected to said second terminal and attached to said'fusible mass and releasable therefrom upon the fusing of the latter, and means responsive to the fusing of said mass for separating said mass and heating conductor.

MORRIS B. WOOD. 

